Fertilization is the process culminating in the union of the maternal and paternal genomes. The successful completion of fertilization, which restores the diploid state necessary for normal development, requires first that the sperm be incorporated into the egg cytoplasm and then that the sperm and egg nuclei migrate together within the egg cytoplasm to achieve syngamy. With the development of new techniques, it is now possible to determine the movements which occur during fertilization, to understand the systems of motility active during each motion, to characterize the configuration in which each motile system is arranged, and to explore the ionic and molecular regulation of each movement. Since most all of the present knowledge on the movements during fertilization is the result of sequences assembled from the study of fixed, and therefore static, micrographs, the first objective of this proposal is to document the actual incorporation of the sperm into the egg and the movements of the sperm and egg nuclei within the cytoplasm which result in pronuclear fusion during fertilization of living mouse and echinoderm zygotes; these motions will be video tape recorded in time lapse using low light illumination with differential interference microscopy of both compressed and spherical eggs. We propose that both microfilaments and microtubules are responsible for movements during the fertilization process; we further propose that microfilaments are responsible for sperm incorporation and that microtubules are motile during the movements of the pronuclei. With the knowledge of the movements occurring in living zygotes, the contractile molecules responsible for each motion will be determined using, at first, selective inhibitors of motility. The direct isolation of cellular structures involved with the movements will permit biochemical characterization of the molecules present. To demonstrate the supramolecular configuration of the motile components, immunofluorescent antibody staining and electron microscopy will be employed. The regulation of the assembly and functioning of each motile apparatus by alterations in ionic and molecular components will be explored. In summary an understanding of the forces which bring the sperm and egg nuclei together during fertilization will be produced.